Rotary power transformer

ABSTRACT

This invention relates to a Rotary Power Transformer, wherein Primary and Secondary windings on a laminated ferromagnetic core are provided, the construction permitting one winding to be rotatable with respect to the remainder of the transformer. This makes possible electrical energization of a rotatable load from a stationary source of electric power, without slip rings or sliding contacts being used. In the application of the invention to a transformer, a laminated ferro-magnetic core having a divided core leg with an air gap between core leg portions is used. A rotatable winding, secondary as a rule, is mechanically coupled to a rotatable hollow shaft passing through the core leg portions and air gap for accommodating leads between the secondary winding and rotatable load, the shaft and load being rotated by some independent means such as a motor. The primary winding is stationary, surrounds the secondary winding, but clears the same for relative rotation. The transformer functions in conventional fashion independently of secondary winding rotation. Any desired power level may be handled by suitable transformer design.

United States Patent 1m Fahrner l Dec. 2, 1975 l l ROTARY POWERTRANSFORMER ]75] Inventor: Charles J. Fahrner, Park Ridge. ill.

[73] Assignee: Johnson Electric Coil C(L, ElmhursL Ill.

22 Filed: Mar. 26. 1975 21 Appl. No; 562,029

[52] U.S. Cl. 323/53; 323/60; 336/l2U; 33(i/l78 [5 l] lnt. Cl. HOIF39/00 [58] Field of Search 336/1 17, H8. ll). I20. 336/178; 323/60. 53

[56] References Cited UNITED STATES PATENTS 3.611230 10/1971 Maake336/l20 Primary E.raminerThomas J. Kozma Attorney Agent, or FirmRobertL. Kahn ABSTRACT This invention relates to a Rotary Power Transformer.

wherein Primary and Secondary windings on a laminated ferromagnetic coreare provided, the construction permitting one winding to be rotatablewith respect to the remainder of the transformer. This makes possibleelectrical energization of a rotatable load from a stationary source ofelectric power, without slip rings or sliding contacts being used. Inthe application of the invention to a transformer, a laminated fer'ro-magnetie core having a divided core leg with an air gap between coreleg portions is used. A rotatable winding, secondary as a rule. ismechanically coupled to a rotatable hollow shaft passing through thecore leg portions and air gap for accommodating leads between thesecondary winding and rotatable load. the shaft and load being rotatedby some independent means such as a motor. The primary winding isstationary. surrounds the secondary winding but clears the same forrelative rotation. The transformer functions in conventional fashionindependently of secondary winding rotation. Any desired power level maybe handled by suitable transformer design.

6 Claims. 7 Drawing Figures US. Patent Dec. 2, 1975 Sheet 1 of23,924,174

U.S. Patent Dc. 2, 1975 Sheet 2 of2 3,924,174

FIG. I

ROTARY POWER TRANSFORMER GENERAL DESCRIPTION OF THE INVENTION otherwinding without the use of sliding contacts such as slip rings. The newtransformer permits direct wire connections between the rotatabletransformer winding and a rotatable load. The transformer embodying theinvention is in practice and in theory a true transformer in thatprimary and secondary windings are coupled through a ferro-magnetic coreto handle any desired level of power characteristic generally of ironcore type of power transformers. For convenience, the primary windingwill be designated as the stationary energizing winding to which a fixedalternating current source can be connected and the secondary winding isthat winding in which potentials are induced by true transformer actionand has currents flow in the secondary in accordance with winding andload parameters. The transformer embodying the present inventionfunctions as a transformer at desired power levels for which thetransformer is designed, irrespective of rotation or lack of rotation ofthe secondary winding. The transformer action is independent of anyrelative rotary movement between the transformer windings. It isunderstood that the secondary winding may be stationary and primarywinding may be rotatable if the energizing source of power happens to berotatable.

The transformer embodying the present invention has a ferro-m agneticcore of flat laminations for providing almost all of a magnetic circuit.An essential feature of the magnetic circuit is a core leg divided intotwo physically separate leg parts having an air gap therebetween, withtransformer windings over the leg parts and gap. The secondary windin gis within a primary winding assembly and extends about the two legportions and air gap. Leads from said secondary winding extend throughthe air gap into an axially disposed hollow rotatable shaft. Thesecondary winding is rotatably coupled to the hollow shaft. The dividedcore leg parts, preferably equally long, are stationary within thesecondary winding and are parts of an otherwise generally conventionallaminated ferro-magnetic transformer core. Disposed about the secondarywinding and clearing the same is a stationary primary winding assembly.

The cross section of the divided leg parts is preferably cruciform inshape, although a simple rectangular shape may be used. A generallycruciform shape, however, is preferred for higher efficiency. The twoleg portions separated by an air gap may be, as an example, part of ashell-type of transformer core, although a simple core type may be used.A stationary frame construction is provided for supporting thestationary parts of the complete transformer and carries suitablebearings in which the centrally disposed rotable tubular shaft iscarried.

The appropriate core stack laminations are suitably fabricated toaccommodate the rotary shaft with sufficient clearance through thestack. The transformer structure may be mounted in a suitable casing orhousing. The rotatable shaft, coupled to the rotatable secondary windingstructure, may be secured in any desired fashion to a suitable rotatableelectric load such as a revolving sign. The transformer secondarystructure, together with the leads within the tubular rotatable shaftand the load, with thus be connected together for rotation. The otherend of the tubular shaft may be solid. Either end may be mechanicallycoupled to an electric motor or other means for rotating the thesecondary winding assembly and load, it being understood thatconventional mechanical engineering design will determine shaftdimensions, bearings, etc. The stationary part of the transformer can behandled in conventional fashion.

Insofar as transformer windings and transformer core design areconcerned, conventional transformer theory and design may generally beapplied with some allowance for the presence of the air gap between thetwo portions of the divided core leg and clearance for rotating parts.Insofar as transformer ratio is concerned, it is possible to have anyvalue. The nature of the load may vary from relatively low voltage loadsto moderately high potentials.

The air gap between the opposed leg portions of the core is required formechanical considerations in connection with coupling of the secondarywinding structure to the hollow shaft. The distance between the opposedends of the divided leg portions may be quite small and in practice maybe of the order of about oneeighth of an inch or more. The air gapshould be large enough to accommodate the rotary physical structurebetween the secondary winding structure and the hollow shaft includinginsulated wire extending from the secondary winding structure to thehollow shaft. It is preferred to have the air gap centrally locatedbetween two equal leg portions.

The speed of rotation of the secondary winding system may range overwide limits, depending upon mechanical considerations. The power levelmay range from any desired minimum, practically about 200 or 300 watts,up to levels in the kilowatt range.

It is understood that the nature of the bearing support for the rotaryshaft will depend upon load factors and may involve such considerationsas end thrust bearings, conventional sleeve bearings, or the like, noneof which will have any substantial effect on the transformer structureitself. Insofar as the nature of clearance between the relativelymovable parts of the transformer are concerned, this will depend uponsuch factors as desired efficiency of the transformer, and generallymechanical factors such as vibration, desired thickness of solidinsulation, speed of rotation, cost and the like.

By virtue of this construction, substantially all leakage lines of forcefrom the magnetic field of the divided leg will link the windings andmaximize efficiency. The magnetic core laminatio ns may utilize variousshapes of laminations, such as for example, E," F," T," L and I toprovide for butt edges or overlapping between separate parts of a singlelamination layer. In accordance with general transformer practice, it isdesirable to have the unavoidable minute air gaps between opposinglamination edges in core layers randomly disposed along various parts ofthe ferro-magnetic circuit to avoid accumulation of minute air gaps atany one particular part of the stack. It is understood, of course, thatthe essential air gap between opposing ends of the divided leg portionsis not included in this avoidance. It is possible to have an E type oflamination for some layers, F shaped parts may be used in other layers,I may be used, the objective being to avoid superimposing any air gapsbetween separate pieces of a lamination layer at any particular part ofthe stack. Inasmuch as this is conventional transformer practice, nodetailed description thereof is necessary.

Due to the selection of a cruciform cross section of the leg portionswithin the secondary winding, care will have to be exercised in stackinglaminations to provide the cruciform section. This may be accomplishedby having different widths of laminations as will be evident later inconnection with the description of the structure. In addition,modification of some laminations will be necessary for accommodating therotary shaft. Generally, it is preferred to have hollow square tubesextending through stack parts on each side of the air gap with therotatable shaft within such rectangular tubes. By providing such asquare tube within each stack part on opposing sides of the air gap, thepositioning of the stack laminations will be facilitated, the outersurface of the square tube providing stops for edges of suchlaminations.

In accordance with customary transformer practice, where laminations areused, the entire stack will generally be divided into two complementarystack portions to permit the disposition of all windings over the coreleg parts and thereafter to interleave such stack parts so that acomplete laminated stack over the windings is provided. Before the stackis assembled, however, the leads for the secondary should be threadedinto the hollow circular shaft to be available for final connection to arotary load. The ends of the tubular shaft extend beyond the transformerproper and are mounted in bearings supported in a frame construction inwhich the entire transformer structure is rigidly secured.

It is normally desirable to improve the power factor of the transformerand to this end, a supplemental primary winding is disposed over theenergizing main primary winding proper, such supplemental windingusually having smaller gauge wire and more turns than the primarywinding proper. The supplemental winding is connected in series with acapacitor and the two are connected across the energized primarywinding. The power factor correction is desirable because of the air gapbetween the opposed, divided core leg portions. The two series connectedwindings constitute a stationary primary winding assembly.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of atransformer embodying the invention disposed within a housing, thetransformer shaft for rotating the winding being shown coupled to arotatable load such as an assembly of incandescent lamps, the view notshowing a driving motor for rotating the transformer shaft;

FIG. 2 is a perspective view of the transformer illustrated in FIG. I,removed from its housing and free from the rotatable load;

FIG. 3 is an elevation on an enlarged scale of a transformer embodyingthe present invention with parts cut away to illustrate certainstructural details thereof;

FIG. 4 is an elevation of a section of a double ended bobbin forcarrying the rotary secondary winding together with the mechanicalcoupling to the rotatable shaft to illustrate the manner in which theleads from the rotatable secondary are taken to the interior of therotatable shaft;

FIG. 5 is a transverse view along line 55 of FIG. 3, showing a laminatedleg about which the secondary rotates;

FIG. 6 is a diagrammatic illustration of the transformer windingstogether with a supplemental primary winding and capacitor for improvingpower factor; and

FIG. 7 is a plan view of a core stack for the new transformer.

DESCRIPTION OF THE PREFERRED SPECIES As illustrated in the drawings anddescribed with reference to the drawings, a shell type of ferro-magneticcore is disclosed. It is understood, however, that except for thedivided core leg about which the transformer windings are positioned,the ferro-magnetic core may assume any one of a number of shapes, thecharacteristics of which and the advantages of which are well known inthe transformer art and may be adopted for reasons generally independentof the application of the invention to provide a new transformer. Beforebeginning the detailed description of the transformer embodying thepresent invention, it will be helpful to consider initially thestructural details of a ferro-magnetic stack consisting of flatlaminations.

Thus, referring to FIGS. 3 and 7, a shell type of transformer core isillustrated wherein leg 10 at one side and leg 11 at the other side hastherebetween a divided transformer leg having portions 12 and 13provided with air gap 14 therebetween. Sides 15 and 16 of the magneticcore completes the ferro-magnetic path. The construction of the dividedferro-magnetic leg consisting of portions 12 and 13 with air gap 14therebetween is essential to the practice of this invention. Otherwiseleg 10 or leg 11 may be omitted, in which case core sides 15 and 16would be limited in length to joining the divided leg and the remainingleg together, with suitable increases in lamination widths. However,from a structural angle and maximize transformer efficiency, thegenerally shell-type core is preferred. A properly dimensionedshell-type transformer core minimizes leakage of magnetic flux from thecore. Centerline 18 extends longitudinally of the divided leg and normalto air gap 14 to indicate an axis of rotation about which the rotatableportions of the transformer turn.

This centerline will naturally pass through the thickness of the stackat core sides 15 and 16, as well as along divided leg portions 12 and 13and through air gap 14. The air gap functions to permit leads to go froma secondary which is normally disposed around divided leg portions 12and 13 and extend radially to centerline l8 and then parallel to thecenterline toward the end of a rotatable shaft to be described later. Itis, therefore, necessary to provide clearance openings in the entirestack and divided leg portions and through air gap 14. The air gap 14between divided core portions 12 and 13 should be just large enough topermit a physical coupling member to extend from the rotatable shaftabout centerline l8 radially outwardly to a cylindrical bobbin memberwhich extends about leg portions 12 and I3 and has sufficient clearanceto permit rotation of the rotary member about divided core leg portions12 and 13. All ferro-magnetic portions of the entire core arestationary. Rotation of a cylindrical secondary assembly is possiblewith respect to the outer surfaces of divided core leg portions 12 and13 on the one hand and the outer space about centerline 18 extendingthrough the entire transformer core and the hollow shaft aboutcenterline 18, which hollow shaft must pass through the entiretransformer core stack, and beyond the same.

For production purposes, it is impractical to make divided leg portions12 and 13 circular in section. Be-

cause of the necessity for the rotary portion of the secondary assemblyto operate, and to provide maximum magnetic efficiency, it is preferredto have the ferromagnetic divided core portions I2 and 13 shaped asillustrated in FIG. 5, to provide a cruciform shape which will clear thecylindrical inner surface of the secondary rotatable winding assembly.The cruciform shape of the leg portions 12 and 13 as well known andwidely used in conventional transformers where windings are prepared oncylindrical bobbins, there being no necessity for any rotationalcharacteristics. The advantages of a cruciform core leg sectionprincipally relate to the fact that the number of different sizedlaminations insofar as the width is concerned, is reduced to two andthus makes the assembly of laminations into a stack possible withminimum trouble and minimum stack sizes and lamination widths.Theoretically, a large number of laminations having graduated leg widthscould be used to provide a generally circular or cylindrical leg or coresection. In practice, the cost of manufacturing and assembling such astack would be prohibitive and would more than outweigh any possibleimprovement in the overall efficiency of the transformer. This isparticularly true in the transformer embodying the present inventionsince clearances for the rotating shaft are also necessary.

The windows in the stack between end legs and 1 1 on the one hand, andthe central divided leg portions 12 and 13 on the other hand, provideroom for both secondary and primary winding assemblies and must alsoinclude clearance for rotation of the secondary winding assembly aboutthe divided core leg portions on the one hand and within the stationaryprimary winding on the other hand. Insofar as the primary windingassembly is concerned, the inside surface thereof considered as aunitary assembly, must be smooth and have sufficient clearance withrespect to the outside of the secondary winding assembly for rotation ofsuch secondary winding assembly. The outside of the primary windingassembly (including an auxiliary winding) will, of course, be within thewindow between the end legs 10 and 11 on the one hand, and the outersurface of the rotatable secondary winding assembly. It will benecessary to anchor the primary winding assembly within the windows torigidly retain such winding assembly in position and permit freerotation of the secondary winding assembly. To this end, spacer bars andmetal curved straps as illustrated, for example, in FIG. 2, may be usedfor firmly maintaining and locking the primary winding assembly inposition.

Center line 18 is the center line for rotatable hollow shaft 20 which inpractice will normally extend not only through an appropriate tunnelthrough the stack of laminations, but beyond so that a rotatable loadfor the transformer secondary can be carried by and rotated with suchhollow shaft 20. In practice, hollow shaft 20 will be mounted withinbearings 22 carried by end plates 23 and 24 adjustably secured to aframe construction illustrated in FIG. 2, to permit centering of hollowshaft 20 for free rotation of the secondary assembly within thetransformer. Hollow shaft 20 may carry a load such as incandescent lampsmounted on base 25, illustrated in FIG. 1, and may also be rotated by asuitable mechanism (not shown) such as an electric motor, for example,which may be directly or indirectly coupled to hollow shaft 20 forrotating the same.

Referring to FIGS. 3 and 4, a unitary construction which, in effect,comprises two cups back-to-back is provided for rotation about dividedcore leg portions 12 and I3 and extending across air gap 14 forms aportion of the rotatable secondary winding assembly. This constructionmay comprise two separate cups back toback, or an integral construction,and has radial clearance openings 29a through the dividing walls of thetwo cup-shaped portions to permit secondary winding insulated wire leadsto extend radially from outside of the cups to the interior of tube 20through at least one aperture in the tube wall. The wire leads extendalong said shaft for connection to the secondary load. Cup-shapedportions 27 and 28 function as a bobbin with coupling portion 29extending radially inwardly and may consist of a strong plastic or othernon-metal about whose outer surface is wound secondary winding 30.

The thickness of secondary winding 30 will be determined by availabledesign space and the electrical details such as the amount of wire, sizeand the like will be determined by generally conventional transformerdesign practice. The outer surface of secondary winding 30 should besmooth and in the event that rotation of the entire winding and shaftassembly is at a substantial speed, then it may be necessary to considerdynamic balance of the rotatable assembly to insure against excessivevibration. The secondary winding should extend for the full length ofthe cupped construction and the secondary winding should be soconstructed to withstand the affect of centrifugal force thereon. Thewire layers may be held tightly in position by suitable means such ascements and the like. It may be desirable for leads from the secondarywinding to be in the form of flat strips covered with a layer ofsuitable insulation to minimize undesirable bulges and it may bedesirable for the sake of balance to take one secondary lead from oneside of the secondary support cup-shaped member and the other lead froma diametrically opposite point of the cup-shaped secondary support.Instead of a solid cup bottom construction for joining cups 27 and 28back-to-back, it is possible to use a spoke construction. In all cases,it is necessary to provide a good mechanical coupling between cups 27and 28 on the one hand and hollow shaft 20 on the other hand, so thatthe shaft can rotate the cup structure without danger or damage.Centrally disposed sleeve portions 31 within each cup portion areprovided for hollow shaft 20 to be snugly disposed to insure goodcoupling. Sleeve portions 31 should not interfere with the secondaryleads.

Since hollow shaft 20 must have a tunnel through the entire stack alongcenter line 18 as illustrated in FIGS. 5 and 7, it is preferred to havecoaxial rigid tubes 35 and 36 disposed on opposite sides of air gap 14and extending to the very outer edges of the laminations define suchtunnel. These tubes are of plastic or other suitable material. Tubes 35and 36 are preferably square, so oriented as to have the sides paralleland perpendicular, respectively, to the laminations to thus provide astop against which laminations may rest. Square tubes 35 and 36 are justenough larger than hollow shaft 20 so that lateral centering of hollowshaft 20 and the secondary rotatable assembly may be accomplished.Hollow shaft 20 itself must be sturdy and may be of steel, or any otherrigid strong material.

It is evident from the geometry of the construction that speciallyshaped laminations, or portions of laminations, may be necessary in thatpart of the stack immediately at square tubes 35 and 36, particularlywhere the edge of a lamination encounters the square side of such atube. The special shapes required for laminations to accommodate thesquare tube will generally be limited to the stack region bordering uponthe square tubes. By designing the relative dimensions of thelaminations (not including thickness) and the square tube portions. thenumber of laminations requiring special fabrication may be reduced to arelatively low proportion. It is evident that a wide variety oflamination shapes such as previously noted may be used. When asubstantial production run of transformers embodying the presentinvention is necessary, standardized lamination shapes required forvarious portions of the stack may be used. The laminations havegenerally conven tional shapes readily available on the market and willbe useful in those stack portions not required to accommodate squaretubes 35 and 36. A generally conventional primary winding structure 37of cylindrical shape is provided about, but clearing rotatable secondary30.

In order to assemble a complete transformer, the entire lamination stackis divided into two stack portions which may be interleaved as inconventional transformer practice after the winding assemblies have beenpositioned over the divided core leg. Thus, for example, stack legportions 10 and 11 may be separable along a plane perpendicular to thestack as seen in FIG. 7, and passing through air gap 14. It is alsopossible to locate the plane or planes of separation at other regions Asis well known, the stack portions have their individual laminationsoverlapping with respect to what has been called a plane of stackseparation, with alter nate laminations extending beyond the plane ofseparation to one side and interleaved when assembled with a similarstack with laminations extending to the other side. In general,separating the entire stack of laminations for accommodating theplacement of the rotatable secondary and stationary primary windings canfollow conventional lines, this procedure being simplitied by the factthat divided core leg portions 12 and 13 are always separated Followingconventional procedure in transformer assembly, the various laminationsare generally provided with holes therethrough at various places toaccommodate bolts for rigidly securing a stack after assembly and afterthe windings have been in place, to form a rigid magnetic core offerro-magnetic laminations. As previously pointed out, it is preferredto have the ends of lamination parts (not including leg portions 12 and13) arranged so that the edges of laminations coming together will bestaggered over the core stack. Where oriented transformer steel is used,it may be desirable to arrange the transformer lamination parts so thatthe lines of magnetic flux extend along the direction of orientation forthe most part.

After the transformer laminations and rotatable parts are assembled. itis preferred to provide a strong frame for securing the stack androtatable portions of the system as well as the stationary primarywinding structure in position to prevent any shift, particularly of thestack and primary winding. To this end, a rigid frame structureincluding side plates 40 and end plates 23 and 24 is provided. Sideplates 40 have retaining strips 41 and 42 and straps 43 and 44 securedto lock the primary winding firmly into position, as shown in FIG. 2,both at the top and bottom of the frame. As pointed out previously, endpiates 23 and 24 have elongated bolt holes to provide a limited degreeof adjustment in all directions so that the rotatable portion of thetransformer may be supported in bearings 22 and properly centered forfree rotation. Bolts or suitable means for locking the end plates inproper position are provided. Bearings 22 may be of any suitable typeand may have means for lubrication. Housing 46 over the transformerillustrated in FIG. 2, may be provided and such housing may have slots47 on opposite walls of the housing to accommodate shaft ends whenpositioning the transformer illustrated in FIG. 2, within the housing.

Due principally to the air gap in the magnetic circuit, it is desirableto improve the power factor of the transformer. Accordingly, anauxilliary winding 50 is connected in series with capacitor 51 acrossthe energizing power source in shunt to the primary winding. Theauxilliary winding 50 may have more turns of substantially finer wiregauge than the principal primary. Auxilliary winding 50 is preferablydisposed over the principal primary winding.

What is claimed is:

l. A transformer having a ferro-magnetic laminated core including a leghaving two aligned leg portions with an air gap therebetween, acylindrical secondary winding structure positioned over said two legportions and air gap so that it is rotatable about the same, a shaftwithin passages through said aligned leg portions and through said airgap and extending through passages in said magnetic core and beyond thecore, means in said air gap securing said secondary winding structure tosaid shaft, said secondary winding having leads extending therefrom andpassing radially in said air gap to said shaft, at least part of saidshaft being hollow from said air gap region to an end of said shaft,said shaft at the region of said air gap having at least one openingthrough its wall to the interior thereof, said secondary winding leadsextending through the shaft wall to the interior thereof and thence tothe end of the hollow shaft portion for connection to a rotatableelectric load, a stationary primary winding having a cylindricalinterior surface disposed about said secondary winding and clearing thesame to permit relative rotation thereof, both of said windings lyingover the leg portions and air gap, means for retaining said corestructure and primary winding rigidly in stationary position, bearingmeans supported by said stationary structure for rotatably supportingthe shaft, said bearing means and support therefor having means foradjusting said shaft means to center the rotatable portions of thetransformer for free rotation, whereby a relatively stationary electricpower source may be metallically connected to the primary winding forenergizing the same and the electric power in said secondary winding maybe directly connected to a rotatable electric load without interpositionof sliding contacts between relatively rotatable parts.

2. The construction according to claim 1, wherein the leg portions ofthe divided leg are shaped to provide a cruciform section for improvingefficiency.

3. The construction according to claim 1, wherein the secondary windingstructure includes a bobbin having the general shape of two cylindricalcups in backto-back relation, said cup bottoms being shaped toaccommodate the rotatable shaft therethrough, said cups being largeenough to clear the outside of the divided magnetic leg portions aboutwhich said cups are adapted to rotate, said cups also having smallsleeve portions through the rotatable shaft passes, said sleeve portionsbeing short enough and thin enough to secure firm adherence to therotatable shaft but clearing the opposed stationary surfaces of the coreleg portions.

4. The construction according to claim 1, wherein passages for therotatable shaft are square in section within the transformer corestructure, said passages being defined by square tubes extending throughthe lamination portions only, the orientation of said square tubes beingsuch that two opposed tube sides are parallel to the length oflaminations while the remaining two opposed tube sides are perpendicularto the edges of laminations, said tubes providing stop limits for theends or sides of laminations, said square tubes being large enough withrespect to the diameter of the shaft so that sufficient clearance isprovided to pennit centering of such shaft with respect to the entiretransformer construction.

5. The construction according to claim 1, wherein means are provided forpower factor correction, said means including an auxiliary primarywinding disposed over the first named primary winding and connectedthrough a capacitor across the primary winding.

6. The construction according to claim 1, wherein a frame constructionis provided for rigidly supporting the core and primary windingstructure in rigid relation to each other and wherein end platesadjustable se cured to said frame are provided for supporting bearingsthrough which the rotatable shaft ends pass, said adjustment permittingproper centering of the rotatable portion of the transformer withrespect to the stationary portion of the transformer.

1. A transformer having a ferro-magnetic laminated core including a leghaving two aligned leg portions with an air gap therebetween, acylindrical secondary winding structure positioned over said two legportions and air gap so that it is rotatable about the same, a shaftwithin passages through said aligned leg portions and through said airgap and extending through passages in said magnetic core and beyond thecore, means in said air gap securing said secondary winding structure tosaid shaft, said secondary winding having leads extending therefrom andpassing radially in said air gap to said shaft, at least part of saidshaft being hollow from said air gap region to aN end of said shaft,said shaft at the region of said air gap having at least one openingthrough its wall to the interior thereof, said secondary winding leadsextending through the shaft wall to the interior thereof and thence tothe end of the hollow shaft portion for connection to a rotatableelectric load, a stationary primary winding having a cylindricalinterior surface disposed about said secondary winding and clearing thesame to permit relative rotation thereof, both of said windings lyingover the leg portions and air gap, means for retaining said corestructure and primary winding rigidly in stationary position, bearingmeans supported by said stationary structure for rotatably supportingthe shaft, said bearing means and support therefor having means foradjusting said shaft means to center the rotatable portions of thetransformer for free rotation, whereby a relatively stationary electricpower source may be metallically connected to the primary winding forenergizing the same and the electric power in said secondary winding maybe directly connected to a rotatable electric load without interpositionof sliding contacts between relatively rotatable parts.
 2. Theconstruction according to claim 1, wherein the leg portions of thedivided leg are shaped to provide a cruciform section for improvingefficiency.
 3. The construction according to claim 1, wherein thesecondary winding structure includes a bobbin having the general shapeof two cylindrical cups in back-to-back relation, said cup bottoms beingshaped to accommodate the rotatable shaft therethrough, said cups beinglarge enough to clear the outside of the divided magnetic leg portionsabout which said cups are adapted to rotate, said cups also having smallsleeve portions through the rotatable shaft passes, said sleeve portionsbeing short enough and thin enough to secure firm adherence to therotatable shaft but clearing the opposed stationary surfaces of the coreleg portions.
 4. The construction according to claim 1, wherein passagesfor the rotatable shaft are square in section within the transformercore structure, said passages being defined by square tubes extendingthrough the lamination portions only, the orientation of said squaretubes being such that two opposed tube sides are parallel to the lengthof laminations while the remaining two opposed tube sides areperpendicular to the edges of laminations, said tubes providing stoplimits for the ends or sides of laminations, said square tubes beinglarge enough with respect to the diameter of the shaft so thatsufficient clearance is provided to permit centering of such shaft withrespect to the entire transformer construction.
 5. The constructionaccording to claim 1, wherein means are provided for power factorcorrection, said means including an auxiliary primary winding disposedover the first named primary winding and connected through a capacitoracross the primary winding.
 6. The construction according to claim 1,wherein a frame construction is provided for rigidly supporting the coreand primary winding structure in rigid relation to each other andwherein end plates adjustable secured to said frame are provided forsupporting bearings through which the rotatable shaft ends pass, saidadjustment permitting proper centering of the rotatable portion of thetransformer with respect to the stationary portion of the transformer.